How to use presets for operator properties?
You can enable presets for an operator using the PRESET option.

eg:

class SomeTool(bpy.types.Operator):
    bl_idname = "object.some_tool"
    bl_label = "Some Tool"
    bl_options = {'PRESET'}

    # - snip -


The preset directory will be set based on the operator name and created on demand.